In accordance with demands for enabling a communication system to operate autonomously, control software installed to a communication apparatus such as an optical cross-connect device, SONET (Synchronous Optical Network)/SDH (Synchronous Digital Hierarchy), a cross-connect device, a router, or an Ethernet switch has become extremely complicated. With the communication apparatus to which such complicated control software is installed, it may become necessary to restart the device when there is a sudden shutdown caused because of malfunctioning of the control software itself or when upgrading the version of the software for expanding the function. In such cases, it is necessary for the communication apparatus to quickly recover the information handled by the control software into the state of before the restart, in order for the communication apparatus to minimize an influence to user traffic that is flown in the communication network.
A part of the information handled by the control software that is installed to a traditional communication apparatus is not stored in a nonvolatile memory but stored in a volatile memory, considering the cost of the memory. Therefore, it is necessary to rebuild the information stored in the volatile memory, when restarting the control software.
The traditional communication apparatus is a device used in a communication network that is shown in FIG. 12, for example, and it is configured with an apparatus control part 51 and a switch part 52. Out of those parts, the communication control part 51 includes a volatile memory 511 and an information converting part 512 as shown in FIG. 13. Here, the volatile memory 511 stores the path information. The information converting part 512 converts switch connecting information (will be described later) and path information obtained from a plurality of external control devices 60 into path information of the device itself, and stores the path information obtained thereby to the volatile memory 511. The switch part 52 stores the switch connecting information to the volatile memory 521. Each of the external control devices 60 has a function of storing the path information and exchanging the path information among #1-#4 communication apparatuses 50 (See Patent Document 1 and Non-Patent Documents 1, 2, for example).
A service control part shown in Patent Document 1 corresponds to the apparatus control part 51, and a service providing part shown in Patent Document 1 corresponds to the switch part 52. Further, information regarding the service control and information regarding service provision shown in Patent Document 1 correspond to the path information and the switch connecting information, respectively.
Furthermore, “node” shown in Non-Patent Document 1 and Non-Patent Document 2 corresponds to the communication apparatus 50, “control plane” shown in Non-Patent Document 1 and Non-Patent Document 2 corresponds to the apparatus control part 51, “RSVP State” shown in Non-Patent Document and Non-Patent Document 2 corresponds to the path information, and “forwarding state” shown in Non-Patent Document 1 and Non-Patent Document 2 corresponds to the switch connecting information. The switch part 52 is not specifically mentioned in Non-Patent Document 1 and Non-Patent Document 2.
Actions of the above-described traditional communication apparatus when it is restarted will be described separately for a case where the #2 communication apparatus 50 provided in the halfway of a path P1 is restarted and for a case where the #1 communication apparatus provided at the start point of the path P1 is restarted.
(1) Actions of Case when #2 Communication Apparatus 50 Provided in Halfway of Path P is Restarted
FIG. 14A is a sequence chart showing the actions of the case where the communication apparatus provided at the halfway point of the path P1 is restarted. FIG. 14B is an illustration showing states of the path P1 in each of the communication apparatuses 50 numbered from #1-#4, when the communication apparatus provided at the halfway point of the path P is restarted. With respect to a restart action, it is assumed here that the apparatus control part 51 rebuilds the path information when a trouble occurs, and the switch part 52 keeps the connected state of the switches.
As shown in FIG. 14A, before the apparatus control part 51 of the #2 communication apparatus 50 is shut down (T1: device shutdown), information of the path P1 is held in all of the #1-#4 communication apparatuses (see (a) of FIG. 14B). In this state, when there is a shutdown because of a malfunction of the control software installed to the apparatus control part 51 of the #2 communication apparatus 50 or other troubles, the apparatus control part 51 of that communication apparatus 50 loses the information of the path P that is stored in the volatile memory (see (b) of FIG. 14B).
Thereafter, the #1 communication apparatus 50 and the #3 communication apparatus 50 as the adjacent devices of the #2 device check a transmitting/receiving state of a Hello message and the like, which are regularly exchanged mutually, so as to detect the fact that the #2 communication apparatus 50 is shut down (T11: trouble detected, T21: trouble detected), and wait for the #2 communication apparatus 50 to restart (see (b) of FIG. 145). When the restart of the #2 communication apparatus 50 is completed (T2: restart completed), updates of the Hello message and the like are started again. Thus, the #1 communication apparatus 50 and the #3 communication apparatus 50 detect the fact that the trouble of the #2 communication apparatus has been recovered (T12: trouble recovery detected, T22: trouble recovery detected). In this state, the apparatus control part 51 of the #2 communication apparatus 50 can check the presence of the apparatus control parts 51 of the #1 and #3 communication apparatuses 50. However, the path information of the path P is not held therein (see (c) of FIG. 14B).
Upon detecting the trouble recovery, the apparatus control part 51 of the #1 communication apparatus 50 that corresponds to a device on the upstream side of the path P1 transmits recovery signaling (RS1) so that the apparatus control part 51 of the #2 communication apparatus 50 can rebuild the information of the path P1. At that time, the control apparatus part 51 of the #3 communication apparatus 50 that corresponds to a device on the downstream side of the path is in a standby state until the recovering signal (RS1) reaches there.
Upon receiving the recovery signaling (RS1) (T3: path reopening started), the apparatus control part 51 of the #2 communication apparatus 50 rebuilds a part (one direction of a bidirectional path) of the path information. Thereafter, the #2 communication apparatus 50 transmits recovery signaling (RS2) to the apparatus control part 51 of the #3 communication apparatus 50. Upon receiving the recovery signaling (RS2), the apparatus control part 51 of the #3 communication apparatus 50 transmits recovery signaling (RS3) to the apparatus control part 51 of the #2 communication apparatus 50 as a response to the recovery signaling (RS2).
Upon receiving it, the apparatus control part 51 of the #2 communication apparatus 50 rebuilds the remainder of the path information (remainder of the bidirectional path), and transmits recovery signaling (RS4) to the #1 communication apparatus 50 thereafter. At the point of completing transmission of the recovery signaling (RS4), rebuilding of the path information in the #2 communication apparatus 50 is completed (T: path preparation completed), and the path information of the path P1 is completely recovered in all the apparatuses as shown in (d) of FIG. 14B.
(2) Actions of Case when #1 Communication Apparatus Provided at Start Point of Path P is Restarted
FIG. 15A is a sequence chart showing the actions of the case where the #1 communication apparatus provided at the start point of the path P1 is restarted. FIG. 15B is an illustration showing states of the path P1 in each of the #1-#4 communication apparatuses 50, when the communication apparatus provided at the start point of the path P1 is restarted. Before the apparatus control part 51 of the #1 communication apparatus 50 is shut down (T1: control software shutdown), information of the path P1 is held in all of the #1-#4 communication apparatuses (see (a) of FIG. 15B).
In this state, when the apparatus control part 51 of the #1 communication apparatus 50 is shut down because of a malfunction of the control software or other troubles, the apparatus control part of the #2 communication apparatus 50 loses the saved information of the path P1 (see (b) of FIG. 15B).
Thereafter, the apparatus control part 51 of the #2 communication apparatus 50 as the adjacent device of the #1 device checks a transmitting/receiving state of a Hello message and the like which are regularly exchanged mutually so as to detect the fact that the #1 communication apparatus 50 is shut down (T11: trouble detected), and waits for the apparatus control part 51 of the #1 communication apparatus 50 to restart (see (b) of FIG. 15B). When the restart of the apparatus control part 51 of the #1 communication apparatus 50 is completed (T2: restart completed), updates of the Hello message and the like are started again. Thus, the #2 communication apparatus 50 detects the fact that the trouble of the #1 communication apparatus 50 has been recovered (T12: trouble recovery detected). In this state, the apparatus control part 51 of the #1 communication apparatus 50 can check the presence of the apparatus control part 51 of the #2 communication apparatus 50. However, the path information of the path P1 is not held therein (see (c) of FIG. 15B).
Upon detecting that the trouble of the #1 communication apparatus is recovered, the apparatus control part 51 of the #2 communication apparatus 50 transmits recovery signaling (RS1) so that the apparatus control part 51 of the #1 communication apparatus 50 can rebuild the information of the path P. Upon receiving the recovery signaling (RS1), the apparatus control part 51 of the #1 communication apparatus 50 rebuilds a part (one direction of a bidirectional path) of the path information, and transmits recovery signaling (RS2) to the apparatus control part 51 of the #2 communication apparatus 50. Upon receiving the recovery signaling (RS2), the apparatus control part 51 of the #2 communication apparatus 50 transmits recovery signaling (RS3) to the apparatus control part 51 of the #1 communication apparatus 50 as a response to the recovery signaling (RS2). With this, the #1 communication apparatus 50 receives the recovery signaling (RS3), and rebuilds the remaining (remainder of the bidirectional path) path information. Thereby, rebuilding of the path information is completed (see (d) of FIG. 15B).
Note here that the actions of a case where there is a trouble in the apparatus control part 51 of the #4 communication apparatus provided at the end point of the path P1 are the same as the above-described case (FIG. 14) where there is a trouble generated at the halfway point, except that the recovery signaling (RS4) is returned without transferring the recovery signaling (RS2, RS3).
Patent Document 1: Japanese Unexamined Patent Publication 2002-84558
Non-Patent Document 1: L. Berger, “Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions,” IETF RFC 3473, January 2003 (Chapter 9, Fault Handling)
Non-Patent Document 2: A. Satyanarayana, et. al. “Extensions to GMPLS RSVP Graceful Restart,” IETF Internet-Draft draft-ietf-ccamp-rsvp-restart-ext-03, June 2005